The invention is an improved extrusion die for forming honeycomb structures. Ceramic material is progressively fed through the die via large feed holes, small feed holes and intersecting slots.
FIGS. 1a and 1b herein are respective side section and top views of a prior art die disclosed in U.S. Pat. No. 4,118,456. The Prior Art die 10 is a laminate formed of a feed body member 12 brazed to an outlet body member 14. A planar parting surface P is formed between opposed faces 34 and 38 of the respective members.
The feed body member 12 has relatively large feed passageways 32 feeding a plurality of relatively small feed holes 22 in the outlet body member 14. A plurality of intersecting slots 16, formed in the outlet body member 14, communicate with, and are fed by, the small feed holes 22. Alternate intersections 18 of the slots 16 are located on center with the small feed holes 22, and are fed thereby. Extrusion material (not shown) is fed from the large feed holes 32 through the small holes 22 and the slots 16 to form a known honeycomb structure.
It can be appreciated from FIG. 1b that each large feed hole 32 feeds a plurality or set of small feed holes 22. However, each large feed hole 32 is not large enough to fully expose, or inscribe within its circumference, the set of small feed holes 22. Thus, a portion 26 of each small feed hole 22 is masked by material forming the inlet body member 12. An unmasked portion 27 of each small feed hole 22 forms a narrow gap G for the passage of extrusion material from the large feed hole 32. Because the gaps G are small, the die is very sensitive to variations in the size of the individual gaps G. Thus, any variation in the size of the gaps G results in major differences in the flow of extrusion material through the individual small feed holes 22 fed thereby. Consequently the honeycomb structure may extrude unevenly.
As the extrusion material passes through each gap G, the flow of said material is restricted. The restriction, or gap G, causes acceleration and compaction of the extrusion material as it moves within the die 10. This causes a relatively high pressure drop across the die 10. Because the pressure drops, more force must be applied to move the extrusion material through the die 10. Extreme forces cause premature die failures. The die 10 also wears severely near sharp corners 28 formed at the interface between the feed body member 12 and the outlet body member 14.
In summary, the flow of material in the prior art device is restricted, causing reduced die life, poor quality ware, and uneven die wear.
The present invention removes the restriction by forming a transition zone in the die. The principle may be extended to dies having more than two body members.
In the present invention, a transition zone is preferably formed by extending either or both the large and small feed holes so that they axially overlap. Extension of the large and small feed holes removes only that material which does not form part of the brazed parting surface. Thus, the laminated strength of the die is substantially unaffected.